The present invention relates to the field of aircraft guidance systems. More specifically, the present invention relates to a system and method for monitoring the ground speed of a descending aircraft.
The interest in developing a global positioning satellite (GPS) sensor as a low-cost alternative to high-grade inertial reference systems (IRS) for various avionics applications has been germinating for some time now. Recently, there has been increased interest in the application of such an alternative to support head-up guidance systems (HGS).
Head-up guidance systems (HGS) are used primarily to enhance a pilot""s situation awareness and provide guidance to pilots during low visibility conditions. With HGS, pilots can focus on external view and read critical flight data from the HGS instead of from the instrument panel. Although HGS can be used during all phases of flight, they are most renowned for providing guidance during approach and landing. Current HGS use instrument landing systems (ILS) for position guidance during approach and landing, and are currently coupled to high-grade inertial reference systems (IRS) to provide display orientation parameters. Attitude heading reference systems (AHRS) can provide some of these parameters with adequate accuracy, but they do not provide ground speed and track angle. An integrated GPS/AHRS function can provide improved attitude accuracy along with ground speed and track angle, but, by itself, the integrity of the ground speed and track angle are tied to the well-known shortcoming of standalone GPS integrity. This shortcoming needs to be rectified with enhancements from information sources external to the integrated GPS/AHRS function itself.
Accordingly, there is a need for a system and method for accurately monitoring the ground speed of a descending aircraft that is completely independent from the GPS function.
The present invention is a system and method for deriving a ground speed of an aircraft on a descent along a flight path. A vertical speed signal is produced as a function of an altitude signal and a vertical acceleration signal. The vertical speed signal is transformed to a nominal ground speed signal based upon a glide slope defined by a glide slope beam. A correction is produced based on a glide slope deviation rate representative of deviation of the aircraft from the glide slope. Based on the nominal ground speed signal and the deviation correction, a corrected ground speed signal is produced. The corrected ground speed signal is filtered with a horizontal acceleration signal and a runway heading signal to produce a smoothed ground speed signal.